The Excommunication Project: Enemy Unknown
by Phalanx
Summary: Diablo might have been sealed within the Black Soulstone, but the Prime Evils were not the only ones interested in subverting humanity for their own purposes. Peace is shattered by an invasion of strange, alien demons, and a desperate Angiris Council appoints the Nephalem to lead the Excommunication Project: Sanctuary's first and only last line of defense against the Ethereal Ones.
1. Secrets of The Ages

**Disclaimer: **This story contains spoilers for XCOM: Enemy Unknown and XCOM: Enemy Within. It also contains spoilers for Diablo III and may contain spoilers for The Reaper of Souls.

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**1. **

**Secrets of the Ages**

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A full moon had passed since the fall of the Prime Evil. An uneasy peace of sorts had settled upon the High Heavens since the Great Invasion of Hell. While the survivors had soldiered on, the way of life for the Seraphim had still changed irrevocably. Even as Tyrael, the Aspect of Wisdom, stood upon the bridge overlooking the Silver City, he could still see the scars of Diablo's rampage, the near-victory of Hell that would have come to pass if it not had been for the heroic efforts of the mortals known as the new Nephalem.

Despite the promise of a brighter future and an alliance between the Nephalem and the Seraphim however, all was not well in the High Heavens. Tyrael might have been appointed The Aspect of Wisdom by the leaders of Heaven, but he knew it was a role not many of the Seraphim could accept a mortal taking on. No, even if that mortal had previously been an angel, the Archangel of Justice himself, no less.

Tyrael frowned. He had no regrets on choosing to give up his Seraphim form to become a mortal. The actions of the Nephalem had proven his choice right, his sacrifice worthy. But still...

He broke out of his dark thoughts when saw the raven coming. The drab mortal creature, looking very out of place in its celestial surroundings, was laboriously making its way through the air, wings working hard to keep aloft. Tyrael knew the creature by sight; the raven had been a companion of one of the Nephalem who had defeated Diablo. Yes, the dour one with the penchant for incendiary explosions, the demon hunter who went by the name of Vrom. As the raven spotted him and purposefully changed course, he wondered what had brought the bird here. Then as it drew closer however, he noticed the heavy burden it carried— a bundle of scrolls, securely wrapped in oilskin.

"What message do you bring from Vrom, my feathered friend?" Tyrael greeted the messenger bird, offering a perch in the form of his shoulder. The weary bird gratefully accepted, and allowed Tyrael to remove its load. Not without some relief too, he imagined; the parcel was comically overlarge for a bird of its size. Vrom was every bit as wordy in his writing as he was with his speech in real life, which made for heavy dispatches, and the poor bird had really had to put in some effort to get its delivery to its intended destination.

Tyrael chuckled as he unrolled the bundle of scrolls, welcoming some news removed from the politics of Heaven and the Angiris Council. He was however, duly surprised when instead of Vrom's usual rambling epistles there was only a relatively short message in the bundle, and the rest of the delivery contained a collection of illustrations. Tyrael glanced at unusually terse note accompanying them:

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_Tyrael,_

_Some new malevolent force has been laying siege to our demon hunters in the Dreadlands. What troubles me is they do not resemble the remnants of the forces of hell after the Prime Evil's defeat, nor do they seem to have any purpose in attacking us that I can comprehend._

_I have included a drawing of the creatures we glimpsed, including the one that was leading the invasion forces. It is quite accurate to how it looks in person. As you know I have a good eye and steady hand for such things. Another thing: I know the feel of demons well, but the power this creature had felt nothing like theirs. This one reminded me of the corrupted angels we encountered when Diablo invaded the Crystal Arch, but without the reek of demonic taint. _

_I do not know how to explain it or what it wants from us, but I intend to find out. I may also choose to find out by the means of filling its head with bolts._

_One more thing: it made a mention of the Angiris Council. If you recognise any of these demons, or who this fallen angel is and why it should choose to command an army of demons against us, please send word by return raven. Corvus, my raven, will find me._

_Your friend,_

_Vrom_

_PS: If this fallen angel is of any importance and if there is any reason why I should **not** fill his angelic head with bolts, also send word by return raven. You might wish to tell Corvus to make haste in that case._

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With chagrined curiosity, Tyrael unrolled one of the parchments containing Vrom's illustrations. The first showed a strange, egg-headed imp-like creature, the second showed a strange aberration that looked like a gargoyle cut in half, and the third showed a prickly spider-creature with spear-like legs. Hideous monstrosities indeed, but nothing that seemed spectacular enough for a Nephalem who had faced the worst of the armies of hell to be worried about.

Then Tyrael picked up the last illustration and froze in recognition. The distinctive visage of an individual long forgotten jumped out at him through the rough but uncannily accurate lines of Vrom's drawing. The parchment crackled as Tyrael involuntarily clenched his fists. It was unmistakable, the shape of that headress-hood, the pattern of those robes... despite himself the former archangel-turned-mortal found himself blurting out a name none of the Angiris Council had uttered for eons, or ever wished to hear of again.

The beauty of the restored Gardens of Hope flashed by unheeded as Tyrael hurried his way to Library of Fate, startling the seraphim he encountered in his mad charge. He did not stop running until he arrived and burst through the doors.

"Itherael!" he managed to gasp out before having to stop for breath so he could continue speaking. There were drawbacks to being restricted to a mortal form. It was only then, when he was still catching his breath, when he became aware of the presence of Auriel, Archangel of Hope, in Itherael's sanctuary as well.

"What has happened, Tyrael?" she asked, looking at him with concern.

He returned her concerned look. Behind her, Itherael, the Archangel of Fate was in a state of great agitation, aimlessly circling with the Scroll of Fate firmly in his grasp. "All of creation bows before the New One, the tyrant overwhelming..." he recited feverishly. "It changes, every iteration darker than the one before it!"

"Tyrael?" Auriel prompted, drawing Tyrael's attention back to her. He quickly realised that he had interrupted her while she was trying to calm Itherael down but chose not to comment on it.

"I came to consult Fate, but it seems he too, has foresight of the ill tidings I bear." He showed Auriel the drawing Vrom had sent him. Just as he had, she recognised him immediately.

"Ubethrael...?"

"Yes," Tyrael said grimly. "He was seen near Arreat, which means that not only have The Ethereal Ones escaped their eternal prison in the Void, they have discovered Sanctuary as well... "

"...and the existence of the Nephalem," Auriel finished for him, her tone grave as she too, understood the implications.

Itherael, still agitated, finally ceased circling and floated back down to join them in discussion.

"If Ubethrael realises what the Nephalem are, and the extent of their potential power, he will no doubt seek them out for another attempt at Ascension."

Tyrael's face was grim as memories of the past surfaced. "We cannot allow Ubethrael to succeed. If he does, there will be nothing left in all creation that can withstand him, or the return of The Ethereal Ones."

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**End of Chapter 1**


	2. This Council Has Appointed You

**2. **

**This Council Has Appointed You**

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"Corvus, what on earth is this thing you have brought me?"

The weary crow turned its head and looked at the human who had spoken and whom it had allied itself with. It cawed before persistently nudging its glittering cargo at its human again. When this did not get the desired reaction, it flapped over, pecked its human on the top of his head as it passed, and flew off in disgust. Vrom the demon hunter, the hero known as The Nephalem, flinched and muttered a curse as the object slipped and fell from his fingers.

Kormac was the swiftest, and caught the item in midair before it hit the ground. "It's a shard of something crystal-like," was his commentary. This elicited a look of annoyance from Vrom. The templar had always been in the habit of stating the obvious.

"I sense some sort of angelic magic emanating from this artifact," Eirena the enchantress said as she took the shard from Kormac and examined it. "I wonder... how does it work?"

"Hell if I know." Vrom was not in a good mood at this point. _That damned Corvus... what was it so mad about?_

"Angels don't write letters, huh?" Lyndon snarked as Eirena continued fiddling with the shard. "I don't see why Ol' Tyrael couldn't just-"

Whatever the scoundrel meant to say about Tyrael was promptly forgotten as Eirena gave a little shriek, which was followed up by Kormac's shout:

"BY ALL THAT IS HOLY!"

All four adventurers whipped out their backup weapons as the shard suddenly flared to life in Eirena's hands. There was a tense moment of silence, but then the light proved to be harmless as an image took form from the glowing light.

"Illusion magic!" muttered Vrom. He had no great love for it, especially after his encounter with Belial, the demon who had been known as The Lord of Lies, and then Azmodan, who had used some similar magic to send some rather futile public disservice messages during the siege of Bastion's Keep. But instead of a demon lord, the ghostly image that appeared before them was that of a heavily-built man. The light was at his back, so all you could see of him was the perfect silhouette of his bald head and broad-set shoulders, but that was more than enough to make an identification.

"Tyrael!"

"Hello, my friend," the silhouette greeted. "I'm glad to see Corvus found you and the vision shard worked. Auriel mentioned there might be some difficulty. I don't have much time, so I must get to the point.

"About the contents of your letter: Yes, I know who is responsible for the attacks: they are an entity we call the Ethereal Ones. Your demon hunters were not alone. I also received word from Ytalea and Li Ming that Ivgorod and Xiansai too, suffered attacks."

"Surely two warriors of their calibre should have been able to take care of the situation?"

"For now, but that is not the worst of it, those demons you encountered in the Dreadlands are but a fraction of their real power. The Ethereal Ones have other weapons, great flying fortresses and arcane constructs that surpass those of the Horadrim at their peak. And worst of all, you were right. The figure you met was a fallen angel- a former member of the Angiris Council."

"What?!"

"A long time ago, long before Inarius ever created Sanctuary, he used to be known as Ubethrael, Archangel of Ambition. But he... turned to dangerous paths. We were forced to excommunicate and imprison him and his followers in the Void to prevent them from carrying out their mad plan for something called 'The Ascension'. It seems that after this long time however, they have escaped."

"Is the Council planning to do something, then?"

"Yes. In light of the recent incursion by the Ethereal Ones, this council has agreed on the initiation of the Excommunication Project. Several of the human nations I still have influence over have convened to take part in it as well. Together with this Council, they have agreed to appoint you to lead the initiative, to oversee humanity's first and last line of defense.

"Your efforts will have considerable influence on the future of Sanctuary, and that of all Creation as well. I urge you to keep that in mind as you proceed on to the new base of operations Isf have arranged for you... er, Vrom?"

Vrom's candid response to Tyrael's speech at this point was a disbelieving sputter.

* * *

From his chamber in the Silver Spire, Tyrael saw the image of Vrom jump to his feet. Even the ghostly echo of him from the vision shard radiated utmost confusion and not a little bit of fury.

"Me?! Wait, why aren't you getting involved at all? Aren't you one of us now? What of the Angiris Council? Are they planning to sit by and do nothing again?"

"Imperius has decreed that the heavenly hosts are not to directly intefere with what goes on in Sanctuary. Council was not able to convince him otherwise."

"Auriel and Itherael didn't see fit to lend their support?"

"It is being debated as we speak. Unfortunately, it seems unlikely we will be able to expend significant resources to aid Sanctuary, Vrom," Tyrael said sadly, as he turned to look out the window. "The Ethereal Ones have already come for us."

There was a stunned pause from the demon hunter. "Tyrael, do you mean to say the High Heavens are under attack again?"

Tyrael did not answer the question. "You must go back to Bastion's Keep, Vrom. We will keep the worst of the Ethereal forces focused upon us. The Ethereal Ones only strike now because they fear we will interfere with what they have planned for you. They intend to enslave humanity for their Ascension, and you are the one who must lead the effort to prevent that at all costs. I will speak to you again about this matter, but I must go now.

"Good luck, my friend."

Thankfully, the vision shard stopped functioning and cut off 'his friend's' colourful objections.

* * *

"I am surprised you chose the reclusive demon hunter as your Commander," Auriel would comment later. "I would have thought some of the other Nephalem would have been far more suitable as a leader of men."

"You are right, if this war could be won by mere flesh, they would have been the ideal choices. But from our skirmishes so far we already know that the power of Ubethrael's forces lies not in his troops, but the fel devices they wield."

Auriel was troubled. "It is true, the green fire artifacts they have empowered their troops with turns even the weakest imp in their ranks into a considerable threat. And those flying fortresses are... formidable."

"Exactly. We have fallen behind The Ethereals in this regard, and I fear Imperius' wrath has blinded him to the importance of it. This war will be won by the side that possesses the greatest mastery of such weapons. That is why the Excommunication Project is so vital to our success.

"In order to defeat our enemy, we must understand them. Of all the Nephalem, Vrom was the only one who made routine use of such knowledge and studied the construction of such artifacts. I think he is the one who would understand this most. I cannot think of a better person to lead the effort to take Ubethrael's weapons from his minions and use them against him."

In the far distance, large shapes tinged with green fire loomed in the skies of the high heavens as flights of angels rose ready to repel the invaders.

Auriel spoke softly as the Angiris Council prepared to do battle. "For the sake of all Creation, I pray for hope that you are right, Tyrael."

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**End of Chapter 2**

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**A/N: **_Originally I'd meant this to be a very different story from what you just read but then I stumbled across this thread in reddit: np. reddit r /Xcom /comments /1s40dv /would_a_medieval_era_xcom_spinoff_work/_

_There was just so much win in the whole thing that I decided then and there that I would rather write a Diablo version of XCOM instead of the __'The Nephalem falls in to XCOM' fic I had planned_.

_So this story is dedicated to the crazy posters, commenters and redditors of that aforementioned thread. Thank you for filling my head with crazy ideas and making me scrap whatever I had of this story to expand that concept instead. This is going to be fun!_

-|P


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